1. Field of the Invention
This invention relates to polymers of maleic anhydride, and, more particularly, to a process of making derivatized maleic anhydride polymers which include maleamic acid and/or its cyclic imide repeat units.
2. Description of the Prior Art
Amines can be reacted with maleic anhydride to give the corresponding half-amide derivative. Generally, a polymer containing maleic anhydride is reacted in solution or suspension with an amine in an inert or non-reactive solvent, such as acetone, heptane, benzene or dibutylether, to provide the desired half-amide derivative. This material then must be isolated and repackaged into a useful product.
Unfortunately, various side reactions occur during such solution or suspension processes. These side reactions adversely affect the quality of the final product, particularly its color and odor. The amine reactant also can form a salt with the half-acid polymer instead of reacting with the anhydride and reduce the yield of the desired amide reaction product.
The reaction of amines with anhydride polymers in an inert solvent also is difficult to control because of its rapid reaction rate and high reaction exotherm leading to the formation of a non-homogeneous reaction product.
Reactions of anhydride polymers with amines in inert solvents present other problems, too. For example, if the reaction is conducted as a slurry, e.g. reaction of p(methyl vinyl ether-maleic anhydride copolymer) with an amine in toluene, the consistency of the slurry may change as the amine reacts with the anhydride polymer. This consistency change usually results in excessive swelling of the polymer during the reaction, which can make subsequent processing very difficult unless the slurry is sufficiently diluted with solvent. However dilution reduces polymer capacity. Reaction of the anhydride polymer as a solution in an inert solvent such as acetone with amine is advantageous but it may result in considerable gelling or precipitation of the reaction product or the formation of "fish eyes".
Similar reactions of anhydride polymers with amines in a reactive solvent such as ethanol may solve these problems because the resultant products are generally made available in the form of homogeneous solution or stable colloidal suspensions which are easy to handle even at a high solids content.
Accordingly, it is an object of this invention to provide a new and improved process of making derivatized maleic anhydride polymers, and, particularly, to a process of making substantially homogeneous maleic anhydride-containing polymers which include maleamic acid and its cyclic imide derivatives.
Another object herein is to provide a process of making polymers containing a maleic anhydride, and its maleamic acid and corresponding cyclic imide derivatives, in a predetermined ratio of each.
A feature of the invention is the provision of such process which is carried out in an alcohol as a reactive solvent.
Another feature of the invention is to control the reaction temperature and period of reaction during the process to predetermine the ratio of each of the maleic anhydride-half-ester, maleamic acid and cyclic imide repeat units of the polymer obtained.
Yet another feature herein is to provide a derivatizing reaction which can be carried forward substantially to completion with little or no unwanted side reactions.
Yet another feature is a derivatization reaction which does not need an esterification or acidification catalyst, and is conducted in a non-toxic solvent.
Among the other features of the invention is the provision of a terpolymer product having little color or odor and little free amine.
These and other objects and features of the invention will be made apparent from the following detailed description of the invention.